This protocol was developed as an effort to characterize new neuromuscular diseases, to learn more about established diseases, to assess current methodologies and technologies and to refine old methods as well as to develop new ones. Using different electrodiagnostic techniques, we have carried a number of different studies: a. Correlation between muscle histology and quantitative electromyography in zidovudine-induced myopathy. We have found that most of the electromyographic abnormalities are not specific for myopathy but correlate with some zidovudine-induced histologic changes (ragged red fibers) and inflammation. b. Electrophysiologic studies in inclusion body myositis to assess for the possibility of a coexistent neurogenic component. Macro- electromyography (macro-EMG) a recently developed technique, that provides information about the territory of the motor unit, has not shown, on a preliminary assessment, evidence of significant reinnervation. c. Reinnervation in clinically unaffected muscles of patients with prior paralytic poliomyelitis: correlation between macro-EMG and histology. We have found a positive correlation between the amplitude of the motor unit potential recorded with the macro-EMG technique and histologic evidence of reinnervation such as fiber-type grouping. d. Electrophysiologic and quantitative sensory studies in patients with Fabry's disease. We have found evidence of predominant involvement of small myelinated axons with sparing of large myelinated axons as assessed with quantitative sensory studies and nerve conduction studies.